Bumper crossmember for a motor vehicle

Abstract

The invention relates to a bumper crossmember (1) for a motor vehicle, comprising a hollow-chamber profile, the hollow-chamber profile having three vertical connection pieces (2, 3, 4) spaced apart from one another in the longitudinal axis direction L of the vehicle, and having upper and lower straps (5, 7; 6, 8) which connect the vertical connection pieces (2, 3, 4) and are spaced apart from one another in the vertical axis direction of the vehicle such that two hollow-chamber zones Z1, Z2 arranged one behind the other in the longitudinal axis direction L and separated by the central vertical connection piece (3) are provided. The invention is particularly characterised in that along its extent in the vertical direction the central vertical connection piece (3) is supported more rigidly against the force-application-side vertical connection piece (2) than the chassis-side vertical connection piece (4) is against the central vertical connection piece (3), such that in the event of a deformation of the bumper crossmember (1) due to a crash force F introduced into the bumper crossmember (1) counter to the direction of travel, the vertical connection pieces (2, 3) of the force-application-side hollow-profile zone Z1 remain substantially spaced apart as a result of the support, while as a result of the deformation the chassis-side vertical connection piece (4) approaches the central contact piece (3) or comes into contact with it, at least in some portions.

Description

[0001] Bumper cross member for a motor vehicle

[0002] The invention relates to a bumper cross member for a motor vehicle having the features of the preamble of claim 1.

[0003] A bumper cross member in a motor vehicle serves to protect the components behind the vehicle and the passenger compartment in the event of a frontal collision. The bumper cross member extends transversely to the vehicle's direction of travel and is positioned in front of the components to be protected. The longitudinal extension of the bumper cross member follows the vehicle's transverse direction. At its lateral ends, the bumper cross member is connected to a longitudinal member of the vehicle, typically a crash box.

[0004] Bumper cross members are used both in the front and rear of a motor vehicle. The present invention is not limited to any specific application.

[0005] When absorbing frontal forces acting on a motor vehicle, whether in a frontal or rear-end collision, the bumper cross member is subjected to bending stresses, particularly due to the desired transmission of the introduced forces to the vehicle's longitudinal member. To accommodate this, bumper cross members feature stiffening structures to prevent bending or buckling, and the associated tearing, as much as possible.

[0006] It is known that such bumper cross members can be designed as a hollow chamber profile. Such a hollow chamber profile is formed from vertical webs and chords connecting the vertical webs, in particular upper and lower chords. The vertical webs and chords enclose one or more hollow chambers that extend essentially in the longitudinal direction of the bumper cross member. By forming hollow chambers, rigid yet lightweight bumper cross members are provided. The bumper cross member can be designed as a shell construction; in this case, one half shell is usually connected to a locking plate, for example, by welding. The use of two half shells joined together is also conceivable.

[0007] In another embodiment, the bumper cross member can be designed as an extruded hollow profile. By providing an extruded profile, complex structures within the bumper cross member, such as additional vertical webs or horizontal support walls, can be incorporated easily and reliably.

[0008] EP 0 718 157 B1 discloses a bumper cross member formed from a hollow chamber profile. This cross member has three vertical webs spaced apart along the longitudinal axis of the motor vehicle, which are connected to each other at their distal ends by upper and lower chords. The vertical web facing the load can be referred to as the force application side vertical web. The vertical web facing away from the load can be referred to as the chassis side vertical web.

[0009] The central vertical web is additionally supported in the center area by the two outer vertical webs using retaining walls, creating four individual hollow chambers. This creates a box profile with uniform internal stiffness. The four hollow chambers can be divided into two hollow chamber zones along the central vertical web: one on the force application side and one on the chassis side.

[0010] DE 601 19 187 T2 discloses a generic stiffening arrangement for a bumper.

[0011] The objective of the disclosure is to ensure that the bumper cross member collapses as evenly as possible in a frontal crash, thus avoiding crack formation. The use of such a bumper cross member is problematic, particularly in light of the increased intrusion length requirements associated with electromobility: Due to the absence of an internal combustion engine, a bumper cross member must be able to absorb significantly greater forces and must not crack even after a significant deformation.

[0012] Based on this problem, the invention is based on the object of providing a bumper cross member which has better performance with regard to its deformation behavior, in particular with large intrusion lengths.

[0013] This object is achieved by a generic bumper cross member as mentioned above with the features of claim 1.

[0014] Advantageous embodiments emerge from the dependent claims and the description.

[0015] The core of the invention is to provide a bumper cross member with two hollow chamber zones arranged one behind the other in the longitudinal direction of the motor vehicle. These zones exhibit different and thus asymmetrical deformation behaviors in the event of a crash. For this purpose, the two hollow chamber zones are designed with different stiffnesses with respect to their area moment of inertia in the load application direction.

[0016] For this purpose, the central vertical web is more rigidly supported against the force-applying vertical web along its respective vertical extension than the chassis-side vertical web is against the central vertical web. Due to the lower support compared to the central vertical web in the longitudinal direction of the vehicle, the chassis-side vertical web buckles more severely in the event of a crash than the central vertical web in the direction of the force-applying vertical web.

[0017] If the bumper cross member deforms due to a frontal crash force acting on it, for example, during a pole test, the bumper cross member—supported by the vehicle's longitudinal members—is loaded as a bending beam. This results in tensile stress peaks on the side facing away from the force application, thus on the chassis side of the bumper cross member, in the longitudinal direction of the bumper cross member, thus in the transverse direction of the vehicle.

[0018] The inventive design of the bumper cross member ensures that, in the event of deformation, the chassis-side vertical web is deformed and buckles in sections due to the applied tensile stress; the chassis-side hollow chamber zone thus collapses at least in sections. Due to the greater stiffening of the central vertical web compared to the force-applied vertical web, the force-applied hollow chamber zone essentially retains its cross-section.

[0019] Against this background, the hollow chamber zone facing the load can also be described as a more buckling-resistant zone, while the hollow chamber zone facing away from the load, on the chassis side, can be described as a more buckling-soft zone.

[0020] Even with large intrusion paths of the bumper cross member, the first hollow chamber zone provides a cross-section that transfers the bending moments through the maintained area moment of inertia, thus ensuring high bending stiffness over the entire intrusion path. In contrast, the second hollow chamber zone supports the transfer of bending at low deformations; with further deformation, the area moment of inertia of the bumper cross member is locally reduced, thus reducing stress peaks on the side of the bumper cross member facing away from the load. This prevents crack formation on the side of the bumper cross member facing away from the load, i.e., the chassis side. At the same time, the deformation of the second hollow chamber zone absorbs crash energy in the manner of a crash box.

[0021] For a specific intrusion path, the chassis-side vertical web may well be intended to abut the center vertical web. The upper and lower chords connecting the chassis-side vertical web to the center vertical web deform accordingly.

[0022] To prevent the belts from tearing, it is preferably provided that the belt connecting the middle web to the chassis-side vertical web is curved with a rounded portion. The radius of this rounded portion is preferably at least twice the wall thickness of the belt in the area of ​​the rounded portion, preferably three times the thickness. If the chassis-side vertical web nestles against the middle web, the belts, particularly if they are designed as a rounded portion, deform like an arched bridge and protrude from the first hollow chamber zone like support ribs or support beads. In this way, they additionally stiffen the first hollow chamber zone for the required flexural rigidity. The rounded portion with the provided radius additionally counteracts any tearing of the belts on their chassis-side side.

[0023] In order to deliberately influence the deformation of the vertical web, the chassis-side vertical web can be provided with a thinner area in the vertical axis direction of the vehicle in an area facing the belt, compared to the central area of ​​the vertical web and the belt. If the chassis-side vertical web deforms towards the central web, inflection points are created by the opposing curvatures - curvature of the belts towards the vertical web in one direction and curvature of the vertical web due to buckling behavior in the other direction. It is advantageous to thin out the vertical web precisely in the area of ​​these inflection points. In contrast, the central area is thickened to ensure the most flat and homogeneous contact area with the central web in the event of deformation.Above this area, forces are also introduced into the central vertical web from the rounded belts, so a particularly large amount of material should be made available here.

[0024] Preferably, the thinned area is thinned in the z-direction in the area facing the belt, in the manner of a jump. Such a jump is not to be understood mathematically, but rather in a professional design sense. The jump essentially discontinuously thins an area that hinges upon movement of the chassis-side vertical web toward the central vertical web. By determining this location relatively precisely, the deformation behavior of the chassis-side vertical web can be specifically influenced.

[0025] In contrast, the central vertical web is supported relative to the vertical web on the force application side, although in the event of deformation, it is understandable that the central vertical web is also deformed to a certain extent, causing it to deflect toward the vertical web on the force application side. However, this deformation is significantly smaller than that of the chassis-side vertical web. The support between the central vertical web and the vertical web on the force application side counteracts the collapse of the front hollow chamber zone.

[0026] The support of the central vertical web relative to the force-applying side can be achieved, for example, by backfoaming the hollow chamber zone facing the load direction. Different heat treatment of the two hollow chamber zones is also conceivable, particularly with regard to the corresponding vertical webs—the central and force-applying vertical web on the one hand, and the chassis-side vertical web on the other. The same applies to a corresponding combination of different materials for the two hollow chamber zones.

[0027] It is also conceivable to differentiate the support of the vertical webs in terms of design: For example, the middle web can be solidly connected to the upper or lower chord that supports the middle vertical web against the vertical web on the force application side, so that the middle vertical web is supported against buckling and prevents significant deformation of the middle vertical web, particularly towards the vertical web on the force application side. The middle vertical web can also have a supporting rib extending vertically from the middle vertical web for stiffening.

[0028] However, it is preferred to provide a supporting wall between the central vertical web and the force-applying vertical web. This supporting wall supports the central vertical web on the force-applying vertical web at a distance from the upper and lower chords, approximately in the middle of the vertical web. This supporting wall thus extends in the longitudinal axis direction of the vehicle and in the longitudinal direction of the bumper cross member. The supporting wall is usually integrally formed on both vertical webs. The supporting wall divides the front hollow chamber zone into two hollow chambers, while the rear hollow chamber zone is preferably designed as a single-chamber zone and extends over the height of the two hollow chambers of the front hollow chamber zone. This support between the central vertical web and the force-applying vertical web is a particularly simple and cost-effective option for highly effective support.

[0029] In one embodiment, it is preferably provided that the supporting wall is tapered along its extension along the longitudinal axis of the vehicle. Due to the vertical expansion of the supporting wall in the region of its respective connection to the vertical webs, the force introduced and transmitted by the supporting wall is distributed evenly into the vertical webs, thus counteracting any buckling of the respective vertical web or tearing of the connection between the supporting wall and the vertical web. In contrast, material has been saved in the central region of the supporting wall in order to provide the lightest possible bumper cross member.

[0030] If a retaining wall is provided in the central region of the central vertical web and the chassis-side vertical web is thickened in its central region, it is preferably provided that the thickening of the chassis-side vertical web is substantially aligned with the longitudinal extension of the retaining wall in a cross-sectional view. This allows the forces introduced into the central vertical web to be transmitted through the retaining wall from the rounded chords in the event of deformation.

[0031] It is also intended that the chord connecting the force application side to the middle vertical web is tapered towards the middle vertical web and, in the area of ​​the connection to the middle vertical web, is aligned with the connection of the chord connecting the middle to the chassis-side vertical web. When the chassis-side vertical web deforms and the associated curvature of the respective upper and lower chords that connect the chassis-side vertical web to the middle vertical web, the connection area to the middle vertical web also acts as a hinge. This hinge effect is uniformed across the entire material by a tapering of the chord connecting the middle to the force application side vertical web in this connection area. This prevents cracks from forming in the hinge area. The respective upper chords and lower chords connecting the vertical websThe lower chords are aligned with each other and thus preferably form an upper and lower chord of the bumper cross member. The vertical webs connecting each other, referred to separately above as upper and lower chords, can then also be referred to as upper and lower chord sections.

[0032] It is preferably provided that the bumper cross member is delimited on the outside by the vertical web on the force application side and on the rear by the vertical web on the chassis side. In the vertical axis direction of the vehicle, the bumper cross member is delimited by the upper chord or lower chord, possibly formed from the upper chord or lower chord sections. This creates a box-shaped bumper cross member.

[0033] Furthermore, it can preferably be provided that the distance between the force application side and the central vertical web is greater than the distance between the central and chassis-side web. The distance between the vertical webs is understood to be in the longitudinal axis direction of the vehicle. In this way, the area moment of inertia of the beam is adjusted such that the center of gravity is shifted from the central vertical web towards the force application side vertical web. This achieves a defined deformation of the central vertical web in the event of deformation, so that the upper and lower chords are deformed essentially uniformly along a large radius in the event of deformation. In this way, a bumper cross member is provided which deforms continuously in the event of deformation. This counteracts the formation of cracks.Preferably, the hollow chamber profile is made of an aluminum alloy, in particular extruded. A hollow chamber profile made of an aluminum alloy is lightweight and allows for high degrees of deformation. However, the degrees of deformation are limited by the fact that this material is prone to cracking under excessive stress peaks, which is completely avoided by the present invention.

[0034] In a further embodiment, at least one stiffening rib extending in the longitudinal direction of the bumper cross member is arranged on the outwardly facing vertical web on the force application side. The stiffening rib protrudes from the vertical web in the direction of the applied crash force and preferably runs essentially along the entire length of the bumper cross member.

[0035] The vertical bar is provided with additional material by the reinforcement rib. The stiffening rib is therefore an addition to the existing vertical bar. The side of the vertical bar facing away from the crash force is therefore essentially flat in the area of ​​the stiffening rib and not curved in the direction of the crash force like a bead. The vertical bar thus forms a basic structure on which the stiffening rib is arranged. The stiffening rib is part of the cross-section of the bumper cross member that absorbs the bending moment.

[0036] In addition, the stiffening rib creates the possibility of influencing the distribution of tensile and compressive stresses along the cross-section of the bumper cross member such that the neutral fiber - i.e. the plane in which the tensile and compressive stresses cancel each other out - can be adjusted with respect to the center of gravity and in particular with respect to the central vertical web. The stiffening ribs offset the neutral fiber towards the force application side. It is preferably provided that the neutral fiber is arranged in the region of the central vertical web, more preferably slightly offset from the force application side. Furthermore, this design of the stiffening rib as an addition to the vertical web as the basic structure allows it to be weakened locally in predetermined sections by reducing the material. The material reduction takes place along the course of the stiffening rib in the longitudinal direction of the bumper cross member.By reducing the material, the area moment of inertia in the cross-section is locally influenced, namely, with respect to the crash force to be absorbed, so that the overall crash behavior can be actively influenced. A material reduction over a short section, approximately 3 to 5 cm along the longitudinal extension of the bumper cross member, is sufficient for this.

[0037] It is particularly preferred to arrange the stiffening ribs on the force-applying vertical web in alignment with the flanges of the hollow profile. This transfers the force directly into the flanges and thus across the entire surface of the bumper cross member.

[0038] Such material weakening can serve to reduce stress peaks in the bumper cross member. For this purpose, a material reduction is provided in particular in the area where the bumper cross member connects to the vehicle's side members, such as the crash boxes. Especially with large intrusion paths, the bumper cross member is at risk of cracking in the area where it connects to the vehicle's side members. Additional stiffening elements, such as a towing sleeve, can also be incorporated into the bumper cross member. Due to the connection to the side member section or the towing sleeve, the bumper cross member is already stiffened by other elements. Additional stiffening by means of the stiffening rib can lead to premature failure of the bumper cross member. The local material reduction in the connection area evens out these stress peaks and distributes them evenly into the material, thus counteracting cracking.For this purpose, in particular, a material reduction is provided over a section that is wider than the connection to the longitudinal member or the crash box. The material reduction extends beyond the connection to the longitudinal member. In another embodiment, it can be provided that the stiffening rib in the center region of the bumper cross member has a material reduction, in particular in at least two regions arranged symmetrically to the center of the bumper cross member. The center of the bumper cross member is to be understood as the center in the longitudinal direction of the bumper cross member, pointing in the vertical direction of the motor vehicle. Here, the material reduction serves to form predetermined bending points that enable a certain deformation during specified tests, such as a pile test.The predetermined buckling points also enable stress peaks in the material, particularly on the side of the bumper cross member facing away from the load, by reducing the section moment of resistance in the reduced material area. Typically, the area of ​​material reduction for such behavior is relatively short, at least shorter than the material reduction in the area where the bumper cross member connects to a side member.

[0039] The invention is explained in more detail with reference to the accompanying figures. They show:

[0040] Fig. 1 : A comparison of the undeformed and the deformed bumper cross member according to the invention in a cross-sectional view,

[0041] Fig. 2 : the undeformed bumper cross member in a cross-sectional view,

[0042] Fig. 3 : the bumper cross member according to the invention in a plan view,

[0043] Fig. 4: the bumper cross member of Figure 3 in a plan view, but deformed after a pile test and

[0044] Fig. 5: the bumper cross member of Figure 1 in a three-dimensional oblique front view.

[0045] The bumper cross member 1 is installed in a vehicle not shown in detail. It is connected to a chassis C not shown in detail via longitudinal members using crash boxes C1, C2. The crash force F acting on the bumper cross member 1 acts on the force application side of the bumper cross member 1.

[0046] Figure 1 shows the bumper cross member 1 in a cross-sectional view in an undeformed (1a) and a deformed (1b) state. The undeformed cross-section is shown in dashed lines, the deformed cross-section in solid lines. Figures 3 and 4 show the bumper cross member 1 in a plan view before (Figure 3) and after (Figure 4) deformation during a pile test. During a pile test, a pile P is pressed onto the front of the bumper cross member 1 with a predetermined force.

[0047] For the sake of clarity, reference is made to Figure 2 below for the details of the cross-section design: The bumper cross member 1 is designed as an extruded hollow chamber profile made of an aluminum alloy and has three vertical webs 2, 3, 4 that are spaced apart from one another in the longitudinal axis direction L of the vehicle and arranged one behind the other when viewed in the direction of travel of the motor vehicle. The middle vertical web 3 is connected by means of upper and lower chords 5, 6, 7, 8 to the force application-side vertical web 2 on the one hand and to the chassis-side vertical web 4 on the other. The vertical webs 2, 3, 4 are thus supported against one another and form two hollow chamber zones Z1, Z2.

[0048] The force application side and thus front hollow chamber zone Z1 is formed by two hollow chambers H1, H2 separated by a supporting wall 9. The chassis side and thus rear hollow chamber zone Z2 is formed by a continuous hollow chamber H3 projecting beyond the two front hollow chambers H1, H2.

[0049] Due to the support wall 9, which is formed in its end areas onto the central vertical web 3 and the force application side vertical web 2, the central vertical web 3 is supported more rigidly relative to the force application side vertical web 2 than the chassis side vertical web 4 is relative to the central vertical web 3. The support wall 9 is waisted (see area P6), so that a flat force introduction occurs from the side of the central vertical web 3 or the force application side vertical web 2.

[0050] The distance between the force application side vertical web 2 and the central vertical web 3 in the longitudinal axis direction L of the motor vehicle is greater than the distance between the central vertical web 3 and the chassis side vertical web 4.

[0051] With reference to Figures 1, 3 and 4, the deformation behavior of the bumper cross member 1 according to the invention is explained in more detail:

[0052] During deformation, tensile forces occur in the chassis-side vertical web 4 due to the expansion in the longitudinal direction of the bumper cross member 1, pointing toward the crash boxes C1, C2. These tensile forces, due to the associated stress peaks, often lead to a tearing of the web facing away from the crash force F, in this case the chassis-side vertical web 4.

[0053] To counteract this, it is provided to provide the chassis-side vertical web 4 facing away from the crash force F with a deformation path in the event of deformation, in that it is supported less relative to the central vertical web 3 than the central vertical web 3 is relative to the force-applied vertical web 2. Due to the lack of support - here: in the central region P5 relative to the central vertical web 3 - the chassis-side vertical web 4 can deform in such a way that its central region P5 rests against the central region 11 of the central vertical web 3. As a result, the central region P5 of the vertical web 4 is supported on the central region 11 of the central vertical web 3. The belts 7, 8 connecting the chassis-side vertical web 4 to the central vertical web 3 are correspondingly deformed in a round shape and represent chassis-side ribs that stiffen the bumper cross member 1 as a whole.The rear hollow chamber zone Z2 has collapsed in this way.

[0054] In contrast, there is the front hollow chamber zone Z1. Due to the retaining wall 9, which stiffens the front hollow chamber zone Z1 and supports the central vertical web 3 against the front vertical web 2 on the force application side, this zone is only slightly deformed and provides a rigid cross-sectional profile even after deformation. The two vertical webs 2, 3 of this hollow chamber zone Z1 remain essentially spaced apart from each other despite the deformation.

[0055] In order to promote the deformation of the chassis-side vertical web 4, an optimized cross-section of the bumper cross member 1 is presented here with reference to Figure 2:

[0056] The chords 7, 8, which connect the chassis-side vertical web 4 to the central vertical web 3, are curved by a rounding (area P3). This rounding has a radius of approximately 20 mm. The chords 7, 8 merge into the chassis-side vertical web 4. This area P3 contains material that stretches and thus thins out as the chassis-side vertical web 4 deforms.

[0057] This area P3 is followed by a sharply thinned area P4. After the deformation of the chassis-side vertical web 4, this thinned area P4 essentially provides the turning point, coming from the curve of the flanges 7, 8 to the oppositely curved central area P5 of the chassis-side vertical web 4. The sharply thinned area provides a defined hinge area.

[0058] In order to relieve the chords 7, 8 with regard to their further curvature during deformation, the chords 5, 6 connecting the central vertical web 3 with the force-applied vertical web 2 are tapered in the area P2 of the connection to the central vertical web 3 (area P1). This tapering also creates a hinge in the area P2 of the transition of the upper chords 5, 7 and lower chords 6, 8 to the connection area of ​​the central vertical web 3, which on the one hand provides rigidity to the front hollow chamber zone Z1, and on the other hand counteracts crack formation due to stress peaks during deformation, in particular of the chassis-side vertical web 4. The bumper cross member 1 shown here is furthermore reinforced by means of three stiffening ribs aligned with the chords 5, 6 and the supporting wall 9.

[0059] 12, 13, 14 are additionally stiffened against bending. The stiffening ribs 12,

[0060] 13. 14 are arranged on the force application side vertical web 2 and thicken the material there in the direction of crash force F. The stiffening ribs

[0061] 12, 13, 14 represent a projecting addition to the vertical web 2 on the force application side.

[0062] As can be seen in Figure 5, the stiffening ribs 12, 13, 14 extend essentially in the longitudinal direction of the bumper cross member 1. The stiffening ribs 12, 14 are arranged in the upper and lower regions, respectively, in the end region of the bumper cross member 1. An additional stiffening rib 13 is arranged centrally with respect to the height of the bumper cross member 1.

[0063] The contour of the stiffening ribs 12, 13, 14 in the direction of the crash force F is straight, providing a flat force introduction surface 15, 16, 17. This avoids point loads.

[0064] The stiffening ribs 12, 13, 14 are formed as solid material in this embodiment. This opens up the possibility of individual local material reduction through machining. In the material-reduced areas M1.1, M1.2, M2.1, M2.2, the respective stiffening ribs 12, 13, 14 are completely interrupted in this embodiment, so that the underlying basic structure in the form of the force-applying vertical web 2 is exposed. As a result of this measure, the bumper cross member 1 is deliberately designed to be softer in these areas M1.1, M1.2, M2.1, M2.2 by reducing the area moment of inertia counter to the crash force F. Local stress peaks are thus avoided, and the introduced crash force F is introduced in a uniformly distributed manner across the bumper cross member 1.

[0065] Thus, in the areas M1 .1 , M1 .2, the stiffening ribs 12,

[0066] 13, 14 to be designed with reduced material over a certain area in which the bumper cross member 1 is connected on the chassis side, for example via crash boxes C1, C2. One crash box C1 of the two crash boxes C1, C2 has, in addition to the connection to the bumper cross member 1, a towing sleeve A. This additionally stiffens the bumper cross member 1 in its connection area. To prevent the bumper cross member 1 from cracking in this area, the additional stiffness of the bumper cross member 1 is compensated for by reducing the material of the bumper cross member 1.

[0067] Also with reference to Figure 3, further areas M2.1, M2.2 of the stiffening ribs 12, 13, 14 have reduced material thickness, specifically in the center of the bumper cross member 1, in at least two areas arranged symmetrically to the center of the bumper cross member. These serve to form predetermined buckling points. In a pile test (see also Figure 4), these improve possible attachment to the pile P shown schematically here, even with large intrusion paths.

[0068] It can also be seen that in the direction of the stiffening ribs 12,

[0069] 13. 14 the transition 18, 19 to the material reduction of the stiffening ribs

[0070] 12. 13. 14 (shown in the figures only as an example) is concavely curved with a radius of at least the projection height V of the stiffening ribs 12, 13, 14 from the force application side vertical web 2.

[0071] The additional stiffening ribs 12, 13, 14 and, in particular, machining or removal in local areas M1.1, M1.2, M2.1, M2.2 of the stiffening ribs 12, 13, 14 create a simple and tool-independent possibility of influencing the area moment of inertia of the bumper cross member 1 in such a way that stress peaks that could result in the bumper cross member 1 cracking are avoided.

[0072] Furthermore, the stiffening ribs 12, 13, 14 provide the ability to influence the distribution of tensile and compressive stresses along the cross-section of the bumper cross member 1 such that the neutral axis—that is, the plane in which the tensile and compressive stresses cancel each other out—can be adjusted relative to the center of gravity and, in particular, relative to the central vertical web 3. The stiffening ribs 12, 13, 14 offset the neutral axis toward the force application side. Preferably, the neutral axis is arranged in the region of the central vertical web 3, more preferably slightly offset from the force application side.

[0073] The invention has been described using an exemplary embodiment. Without departing from the scope of protection defined by the applicable claims, numerous further embodiments for implementing the inventive concept will become apparent to those skilled in the art without the need for further explanation within the scope of these statements.

[0074] List of reference symbols

[0075] 1 bumper cross member

[0076] 2 vertical webs on the force application side

[0077] 3 middle vertical bar

[0078] 4 chassis-side vertical bar

[0079] 5. 7 Upper chord

[0080] 6. 8 Lower chord

[0081] 9 Retaining wall

[0082] P5 Center area of ​​the chassis-side vertical bar

[0083] 1 1 Central area of ​​the central vertical bar

[0084] 12, 13, 14 stiffening rib

[0085] 15, 16, 17 Force introduction area

[0086] 18, 19 Transition

[0087] V Stiffening rib projection height

[0088] P1 to P6 range

[0089] Z1 , Z2 hollow chamber zone

[0090] M1.1 , M1.2, M2.1 , M2.2 Material-reduced areas

[0091] H1, H2, H3 hollow chamber

[0092] C Chassis

[0093] C1, C2 crash box

[0094] A towing sleeve

[0095] L Longitudinal axis direction of motor vehicle

[0096] P Post

[0097] F Crash force

Claims

Patent claims 1. Bumper cross member (1) for a motor vehicle, comprising a hollow chamber profile, the hollow chamber profile comprising three vertical webs (2, 3, 4) spaced apart from one another in the longitudinal axis direction (L) of the vehicle, as well as upper and lower chords (5, 7; 6, 8) connecting the vertical webs (2, 3, 4) and spaced apart from one another in the vertical axis direction of the vehicle, so that two hollow chamber zones (Z1, Z2) arranged one behind the other in the longitudinal axis direction (L) are provided, separated by the central vertical web (3), wherein along its extension in the vertical direction, the central vertical web (3) is supported more rigidly against the force application side vertical web (2) than the chassis side vertical web (4) against the central vertical web (3), so that in the event of a deformation of the bumper cross member (1) due to a crash force (F) introduced into the bumper cross member (1) against the direction of travel, the vertical webs (2,3) the force application side hollow chamber zone (Z1) remain spaced apart essentially due to the support, while the chassis-side vertical web (4) at least approaches the central vertical web (3) in sections as a result of the deformation or contacts it, characterized in that the belt (5, 6) connecting the force application side (2) to the central vertical web (3) is tapered towards the central vertical web (3) and in the region (P2) of the connection to the central vertical web (3) is aligned with the connection of the belt (7, 8) connecting the central (3) to the chassis-side vertical web (4).

2. Bumper cross member according to claim 1, characterized in that the hollow chamber profile is provided from an aluminum alloy.

3. Bumper cross member according to one of claims 1 to 2, characterized in that for supporting the central vertical web (3) against the force-applying vertical web (2) between the two vertical webs (2, 3) an additional supporting wall (9) extending in the longitudinal axis direction (L) of the vehicle is provided, approximately centrally relative to the extension of the vertical webs (2, 3) in the vertical direction.

4. Bumper cross member according to claim 3, characterized in that the supporting wall (9) is waisted in its extension pointing in the longitudinal axis direction (L) of the vehicle.

5. Bumper cross member according to one of claims 1 to 4, characterized in that the belt (7, 8) connecting the middle (3) with the chassis-side vertical web (4) is curved with a rounding.

6. Bumper cross member according to one of claims 1 to 5, characterized in that the chassis-side vertical web (4) has, in the vertical axis direction of the vehicle, in a region (P4) facing the belt (7, 8), a region (P4) which is thinned out compared to the central region (P5) of the vertical web (4) and the belt (7, 8).

7. Bumper cross member according to claim 6, characterized in that the thinned region (P4) is thinned in the z-direction in its region facing the belt (7, 8) in the manner of a jump.

8. Bumper cross member according to one of claims 1 to 7, characterized in that the distance between the force application side (2) and the central vertical web (3) is greater than the distance between the central (3) and chassis side (4) vertical web.

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